Environmental barrier coatings providing cmas mitigation capability for ceramic substrate components

ABSTRACT

Environmental barrier coatings having CMAS mitigation capability for silicon-containing components. In one embodiment, the barrier coating includes a bond coat layer comprising silicon or silicide, and an outer layer selected from the group consisting of Ln 4 Al 2 O 9 , and Lna 4 Ga 2 O 9 .

TECHNICAL FIELD

Embodiments described herein generally relate to environmental barriercoatings (EBCS) providing CMAS mitigation capability for use withceramic substrate components.

BACKGROUND OF THE INVENTION

Higher operating temperatures for gas turbine engines are continuouslybeing sought in order to improve their efficiency. However, as operatingtemperatures increase, the high temperature durability of the componentsof the engine must correspondingly increase. Significant advances inhigh temperature capabilities have been achieved through the formulationof iron, nickel, and cobalt-based superalloys. While superalloys havefound wide use for components used throughout gas turbine engines, andespecially in the higher temperature sections, alternativelighter-weight substrate materials have been proposed.

Ceramic matrix composites (CMCs) are a class of materials that consistof a reinforcing material surrounded by a ceramic matrix phase. Suchmaterials, along with certain monolithic ceramics (i.e. ceramicmaterials without a reinforcing material), are currently being used forhigher temperature applications. Using these ceramic materials candecrease the weight, yet maintain the strength and durability, ofturbine components. Furthermore, since these materials have highertemperature capability than metals, significant cooling air savings canbe realized that increase the efficiency of a turbine engine. Therefore,such materials are currently being considered for many gas turbinecomponents used in higher temperature sections of gas turbine engines,such as airfoils (e.g. turbines, and vanes), combustors, shrouds andother like components that would benefit from the lighter-weight andhigher temperature capability these materials can offer.

CMC and monolithic ceramic components can be coated with EBCs to protectthem from the harsh environment of high temperature engine sections.EBCs can provide a dense, hermetic seal against the corrosive gases inthe hot combustion environment. In dry, high temperature environments,silicon-based (nonoxide) CMCs and monolithic ceramics undergo oxidationto form a protective silicon oxide scale. However, the silicon oxidereacts rapidly with high temperature steam, such as found in gas turbineengines, to form volatile silicon species. This oxidation/volatilizationprocess can result in significant material loss, or recession, over thelifetime of an engine component. This recession also occurs in CMC andmonolithic ceramic components comprising aluminum oxide, as aluminumoxide reacts with high temperature steam to form volatile aluminumspecies as well.

Currently, most EBCs used for CMC and monolithic ceramic componentsconsist of a three-layer coating system generally including a bond coatlayer, at least one transition layer applied to the bond coat layer, andan optional outer layer applied to the transition layer. Optionally, asilica layer may be present between the bond coat layer and the adjacenttransition layer. Together these layers can provide environmentalprotection for the CMC or monolithic ceramic component.

More specifically, the bond coat layer may comprise silicon and maygenerally have a thickness of from about 0.5 mils to about 6 mils. Forsilicon-based nonoxide CMCs and monolithic ceramics, the bond coat layerserves as an oxidation barrier to prevent oxidation of the substrate.The silica layer may be applied to the bond coat layer, or alternately,may be formed naturally or intentionally on the bond coat layer. Thetransition layer may typically comprise mullite, barium strontiumaluminosilicate (BSAS), a rare earth disilicate, and variouscombinations thereof, while the optional outer layer may comprise BSAS,a rare earth monosilicate, and combinations thereof. There may be from 1to 3 transition layers present, each layer having a thickness of fromabout 0.1 mils to about 6 mils, and the optional outer layer may have athickness of from about 0.1 mils to about 40 mils.

Each of the transition and outer layers can have differing porosity. Ata porosity of about 10% or less, a hermetic seal to the hot gases in thecombustion environment can form. From about 10% to about 40% porosity,the layer can display mechanical integrity, but hot gases can penetratethrough the coating layer damaging the underlying EBC. While it isnecessary for at least one of the transition layer or outer layer to behermetic, it can be beneficial to have some layers of higher porosityrange to mitigate mechanical stress induced by any thermal expansionmismatch between the coating materials and the substrate.

Unfortunately, deposits of calcium magnesium aluminosilicate (CMAS) havebeen observed to form on components located within higher temperaturesections of gas turbine engines, particularly in combustor and turbinesections. These CMAS deposits have been shown to have a detrimentaleffect on the life of thermal barrier coatings, and it is known thatBSAS and CMAS chemically interact at high temperatures, i.e. above themelting point of CMAS (approximately 1150° C. to 1650° C.). It is alsoknown that the reaction byproducts formed by the interaction of BSAS andCMAS are detrimental to EBCs as well as being susceptible tovolatilization in the presence of steam at high temperatures. Suchvolatilization can result in the loss of coating material and protectionfor the underlying component. Thus, it is expected that the presence ofCMAS will interact with the EBC, thereby jeopardizing the performance ofthe component along with component life.

Accordingly, there remains a need for novel environmental barriercoatings that provide CMAS mitigation capability for use in conjunctionwith ceramic substrate components.

BRIEF DESCRIPTION OF THE INVENTION

Embodiments herein generally relate to environmental barrier coatingshaving CMAS mitigation capability for silicon-containing components, thebarrier coating comprising: a bond coat layer comprising silicon orsilicide; and an outer layer selected from the group consisting ofLn₄Al₂O₉, and Lna₄Ga₂O₉.

Embodiments herein also generally relate to environmental barriercoatings having CMAS mitigation capability for silicon-containingcomponents, the barrier coating comprising: a bond coat layer comprisingsilicon or silicide; a transition layer comprising HfO2 or LnPO4; and anouter layer selected from the group consisting of Ln4Al2O9, Ln4Ga2O9,AeZrO3, AeHfO3, ZnAl2O4, MgAl2O4, Ln3Ga5O12, Ln2Al5O12, AeAl12O19, andGa2O3.

Embodiments herein also generally relate to environmental barriercoatings having CMAS mitigation capability for silicon-containingcomponents, the barrier coating comprising: a bond coat layer comprisingsilicon or silicide; a transition layer comprising Ln4Al2O9 orLna4Ga2O9; and an outer layer selected from the group consisting ofLn2SiO5, AeZrO3, AeHfO3, ZnAl2O4, MgAl2O4, Ln3Ga5O12, Ln2Al5O12,AeAl12O19, Ga2O3, BSAS, HfO₂, and LnPO₄.

Embodiments herein also generally relate to environmental barriercoatings having CMAS mitigation capability for silicon-containingcomponents, the barrier coating comprising: a bond coat comprisingsilicon or silicide; a first transition layer selected from the groupconsisting of Ln4Al2O9, and Lna4Ga2O9; a second transition layerselected from the group consisting of AeAl12O19, and BSAS; and an outerlayer wherein when the second transition layer is AeAl12O19 the outerlayer is AeAl4O7 and wherein when the second transition layer is BSASthe outer layer is ZnAlO4, or MgAl2O4.

Embodiments herein also generally relate to environmental barriercoatings having CMAS mitigation capability for silicon-containingcomponents, the barrier coating comprising: a bond coat comprisingsilicon or silicide; a first transition layer selected from HfO2, orLnPO4; a second transition layer comprising AeAl12O19; and an outerlayer comprising AeAl4O7.

Embodiments herein also generally relate to environmental barriercoatings having CMAS mitigation capability for silicon-containingcomponents, the barrier coating comprising: a bond coat layer comprisingsilicide; a first transition layer comprising Ln2Si2O7; a secondtransition layer comprising BSAS; and an outer layer comprising ZnAl2O4.

Embodiments herein also generally relate to environmental barriercoatings having CMAS mitigation capability for silicon-containingcomponents, the barrier coating comprising: a bond coat layer comprisingsilicide; a transition layer comprising Ln₂Si₂O₇; and an outer layerselected from the group consisting of Ln₄Ga₂O₉, or Ln₃Ga₅O₁₂.

These and other features, aspects and advantages will become evident tothose skilled in the art from the following disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

While the specification concludes with claims particularly pointing outand distinctly claiming the invention, it is believed that theembodiments set forth herein will be better understood from thefollowing description in conjunction with the accompanying figures, inwhich like reference numerals identify like elements.

FIG. 1 is a schematic cross sectional view of one embodiment of anenvironmental barrier coating providing CMAS mitigation in accordancewith the description herein.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments described herein generally relate to EBCs providing CMASmitigation capability for ceramic substrate components.

The environmental barrier coatings having CMAS mitigation capabilitydescribed herein may be suitable for use in conjunction with substratescomprising CMCs, and monolithic ceramics. As used herein, “CMCs” refersto silicon-containing, or oxide-oxide, matrix and reinforcing materials.Some examples of silicon-containing CMCs acceptable for use herein caninclude, but should not be limited to, materials having a matrix andreinforcing fibers comprising non-oxide silicon-based materials such assilicon carbide, silicon nitride, silicon oxycarbides, siliconoxynitrides, and mixtures thereof. Examples include, but are not limitedto, CMCs with silicon carbide matrix and silicon carbide fiber; siliconnitride matrix and silicon carbide fiber; and silicon carbide/siliconnitride matrix mixture and silicon carbide fiber. Furthermore, CMCs canhave a matrix and reinforcing fibers comprised of oxide ceramics. Theseoxide-oxide composites are described below.

Specifically, the “oxide-oxide CMCs” may be comprised of a matrix andreinforcing fibers comprising oxide-based materials such as aluminumoxide (Al₂O₃), silicon dioxide (SiO₂), aluminosilicates, and mixturesthereof. Aluminosilicates can include crystalline materials such asmullite (3Al₂O₃ 2SiO₂), as well as glassy aluminosilicates.

As used herein, “monolithic ceramics” refers to materials comprisingonly silicon carbide, only silicon nitride, only alumina, or onlymullite. Herein, CMCs and monolithic ceramics are collectively referredto as “ceramics.”

As used herein, the term “barrier coating(s)” refers to environmentalbarrier coatings (EBCs). The barrier coatings herein may be suitable foruse on ceramic substrate components 10 found in high temperatureenvironments, such as those present in gas turbine engines. “Substratecomponent” or simply “component” refers to a component made from“ceramics,” as defined herein.

More specifically, as explained herein below, EBC 12 may comprise anoptional bond coat layer 14, an optional silica layer 15, optionally atleast one transition layer 16, and an outer layer 18, as shown generallyin FIG. 1. The bond coat layer 14 may comprise silicon, silicide,aluminide, or aluminide with a thermally grown aluminide oxide scale(henceforth “aluminide-alumina TGO”). By “thermally grown” it is meantthat the intermetallic aluminde layer is applied to the CMC, then analuminum oxide layer forms on top of the deposited aluminide layer aftersubsequent thermal exposure. As used herein “silicide” may include, butis not limited to, niobium disilicide, molybdenum disilicide, rare earth(Ln) silicides, nobel metal silicides, chromium silicide (e.g. CrSi₃),niobium silicide (e.g. NbSi₂, NbSi₃), molybdenum silicide (e.g. MoSi₂,MoSi₃), tantalum silicide (e.g. TaSi₂, TaSi₃), titanium silicide (e.g.TiSi₂, TiSi₃), tungsten silicide (e.g. WSi₂, W₅Si₃), zirconium silicide(e.g. ZrSi₂), hafnium silicide (e.g. HfSi₂),

As used herein, “Ln” refers to the rare earth elements of scandium (Sc),yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium(Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd),terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm),ytterbium (Yb), lutetium (Lu), and mixtures thereof, while “Lna” refersto the rare earth elements of lanthanum (La), cerium (Ce), praseodymium(Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu),gadolinium (Gd), and mixtures thereof.

More particularly, as used herein, “rare earth silicides” may includescandium silicide (e.g. ScSi₂, Sc₅Si₃, Sc₃Si₅, ScSi, Sc₃Si₄), yttriumsilicide (e.g. YSi₂, Y₅Si₃, Y₃Si₅, YSi, Y₃Si₄), lanthanum silicide (e.g.LaSi₂, La₅Si₃, La₃Si₅, LaSi, La₃Si₄), cerium silicide (e.g. CeSi₂,Ce₅Si₃, Ce₃Si₅, CeSi, Ce₃Si₄), praseodymium silicide (e.g. PrSi₂,Pr₅Si₃, Pr₃Si₅, PrSi, Pr₃Si₄), neodymium silicide (e.g. NdSi₂, Nd₅Si₃,Nd₃Si₅, NdSi, Nd₃Si₄), promethium silicide (e.g. PmSi₂, Pm₅Si₃, Pm₃Si₅,PmSi, Pm₃Si₄), samarium silicide (e.g. SmSi₂, Sm₅Si₃, Sm₃Si₅, SmSi,Sm₃Si₄), europium silicide (e.g. EuSi₂, Eu₅Si₃, Eu₃Si₅, EuSi, Eu₃Si₄,Eu₃Si₄), gadolinium silicide (e.g. GdSi₂, Gd₅Si₃, Gd₃Si₅, GdSi, Gd₃Si₄),terbium silicide (e.g. TbSi₂, Tb₅Si₃, Tb₃Si₅, TbSi, Tb₃Si₄), dysprosiumsilicide (DySi₂, Dy₅Si₃, Dy₃Si₅, DySi, Dy₃Si₄), holmium silicide (HoSi₂,Ho₅Si₃, Ho₃Si₅, HoSi, Ho₃Si₄), erbium silicide (ErSi₂, Er₅Si₃, Er₃Si₅,ErSi, Er₃Si₄), thulium silicide (TmSi₂, Tm₅Si₃, Tm₃Si₅, TmSi, Tm₃Si₄),ytterbium silicide (e.g. YbSi₂, Yb₅Si₃, Yb₃Si₅, YbSi, Yb₃Si₄), lutetiumsilicide (e.g. LuSi₂, Lu₅Si₃, Lu₃Si₅, LuSi, Lu₃Si₄), and mixturesthereof. It should be noted that only non-oxide, silicon-basedmonolithic ceramics and composites require a bond coat.

Also, as used herein throughout, “aluminides” may include, but shouldnot be limited to, ruthenium aluminide, platinum aluminide, nickelaluminide, titanium aluminide, or mixtures thereof.

When a silicon-containing component is selected, the bond coat layer 14may comprise any of a silicon bond coat layer, a silicide bond coatlayer, or an aluminide-alumina TGO bond coat layer, each of which isdescribed herein below. As used herein throughout, “silicon-containingcomponent” includes silicon-containing CMCs, monolithic silicon carbideceramics and monolithic silicon nitride ceramics.

In one embodiment, a silicon-containing component may have a siliconbond coat layer 14. In this instance, the EBC may comprise one of thefollowing architectures: a silicon bond coat layer 14, an optionalsilica layer 15, and a Ln4Al₂O₉ outer layer 18; a silicon bond coatlayer 14, an optional silica layer 15, and a Lna₄Ga₂O₉ outer layer 18; asilicon bond coat layer 14, an optional silica layer 15, a HfO₂transition layer 16, and a Ln₄Al₂O₉ outer layer 18; a silicon bond coatlayer 14, an optional silica layer 15, a HfO₂ transition layer 16, and aLn₄Ga₂O₉ outer layer 18; a silicon bond coat layer 14, an optionalsilica layer 15, a LnPO₄ transition layer 16, and a Ln₂SiO₅ outer layer18; a silicon bond coat layer 14, an optional silica layer 15, a LnPO₄transition layer 16, and a Ln₂Si₂O₇ outer layer 18; a silicon bond coatlayer 14, an optional silica layer 15, a LnPO₄ transition layer 16, anda Ln₄Al₂O₉ outer layer 18; a silicon bond coat layer 14, an optionalsilica layer 15, a LnPO₄ transition layer 16, and a Ln₄Ga₂O₉ outer layer18; a silicon bond coat layer 14, an optional silica layer 15, aLn₄Al₂O₉ transition layer 16, and a Ln₂SiO₅ outer layer 18; a siliconbond coat layer 14, an optional silica layer 15, a Lna₄Ga₂O₉ transitionlayer 16, and a Ln₂SiO₅ outer layer 18; a silicon bond coat layer 14, anoptional silica layer 15, a LnPO4 transition layer 16, and a Ln₂SiO₅outer layer 18; a silicon bond coat layer 14, an optional silica layer15, a Ln₄Al₂O₉ transition layer 16, and a AeZrO₃ outer layer 18; asilicon bond coat layer 14, an optional silica layer 15, a Ln₄Al₂O₉transition layer 16, and a HfO₂ outer layer 18; a silicon bond coatlayer 14, an optional silica layer 15, a Ln₄Al₂O₉ transition layer 16,and a LnPO₄ outer layer 18; a silicon bond coat layer 14, an optionalsilica layer 15, a Lna₄Ga₂O₉ transition layer 16, and a HfO₂ outer layer18; a silicon bond coat layer 14, an optional silica layer 15, aLna₄Ga₂O₉ transition layer 16, and a LnPO₄ outer layer 18; a siliconbond coat layer 14, an optional silica layer 15, a Ln₄Al₂O₉ transitionlayer 16, and a AeHfO₃ outer layer 18; a silicon bond coat layer 14, anoptional silica layer 15, a Lna₄Ga₂O₉ transition layer 16, and a AeZrO₃outer layer 18; a silicon bond coat layer 14, an optional silica layer15, a Lna₄Ga₂O₉ transition layer 16, and a AeHfO₃ outer layer 18; asilicon bond coat layer 14, an optional silica layer 15, a HfO₂transition layer 16, and a AeZrO₃ outer layer 18; a silicon bond coatlayer 14, an optional silica layer 15, a HfO₂ transition layer 16, and aAeHfO₃ outer layer 18; a silicon bond coat layer 14, an optional silicalayer 15, a LnPO₄ transition layer 16, and a AeZrO₃ outer layer 18; asilicon bond coat layer 14, an optional silica layer 15, a LnPO₄transition layer 16, and a AeHfO₃ outer layer 18; a silicon bond coatlayer 14, an optional silica layer 15, a HfO₂ transition layer 16, and aZnAl₂O₄ outer layer 18; a silicon bond coat layer 14, an optional silicalayer 15, a LnPO₄ transition layer 16, and a ZnAl₂O₄ outer layer 18; asilicon bond coat layer 14, an optional silica layer 15, a Ln₄Al₂O₉transition layer 16, and a ZnAl₂O₄ outer layer 18; a silicon bond coatlayer 14, an optional silica layer 15, a Lna₄Ga₂O₉ transition layer 16,and a ZnAl₂O₄ outer layer 18; a silicon bond coat layer 14, an optionalsilica layer 15, a HfO₂ transition layer 16, and a MgAl₂O₄ outer layer18; a silicon bond coat layer 14, an optional silica layer 15, a LnPO₄transition layer 16, and a MgAl₂O₄ outer layer 18; a silicon bond coatlayer 14, an optional silica layer 15, a Ln₄Al₂O₉ transition layer 16,and a MgAl₂O₄ outer layer 18; a silicon bond coat layer 14, an optionalsilica layer 15, a Lna₄Ga₂O₉ transition layer, and a MgAl₂O₄ outerlayer; a silicon bond coat layer 14, an optional silica layer 15, aLn₂Si₂O₇ first transition layer, a Ln₂SiO₅ second transition layer, anda Ln₃Ga₅O₁₂ outer layer; a silicon bond coat layer 14, an optionalsilica layer 15, a HfO₂ transition layer, and a Ln₃Ga₅O₁₂ outer layer; asilicon bond coat layer 14, an optional silica layer 15, a LnPO₄transition layer, and a Ln₃Ga₅O₁₂ outer layer; a silicon bond coat layer14, an optional silica layer 15, a Ln₄Al₂O₉ transition layer, and aLn₃Ga₅O₁₂ outer layer; a silicon bond coat layer 14, an optional silicalayer 15, a Lna₄Ga₂O₉ transition layer and a Ln₃Ga₅O₁₂ outer layer; asilicon bond coat layer 14, an optional silica layer 15, a Ln₂Si₂O₇first transition layer, a Ln₂SiO₅ second transition layer, and aLn₃Al₅O₁₂ outer layer; a silicon bond coat layer 14, an optional silicalayer 15, a HfO₂ transition layer, and a Ln₃Al₅O₁₂ outer layer; asilicon bond coat layer 14, an optional silica layer 15, a LnPO₄transition layer, and a Ln₃Al₅O₁₂ outer layer; a silicon bond coat layer14, an optional silica layer 15, a Ln₄Al₂O₉ transition layer, and aLn₃Al₅O₁₂ outer layer; a silicon bond coat layer 14, an optional silicalayer 15, a Lna₄Ga₂O₉ transition layer, and a Ln₃Al₅O₁₂ outer layer; asilicon bond coat layer 14, an optional silica layer 15, a HfO₂transition layer, and a AeAl₁₂O₁₉ outer layer; a silicon bond coat layer14, an optional silica layer 15, a LnPO₄ transition layer, and aAeAl₁₂O₁₉ outer layer; a silicon bond coat layer 14, an optional silicalayer 15, a Ln₄Al₂O₉ transition layer, and a AeAl₁₂O₁₉ outer layer; asilicon bond coat layer 14, an optional silica layer 15, a Lna₄Ga₂O₉transition layer, and a AeAl₁₂O₁₉ outer layer; a silicon bond coat layer14, an optional silica layer 15, a HfO₂ transition layer, a AeAl₁₂O₁₉transition layer, and a AeAl₄O₇ outer layer; a silicon bond coat layer14, an optional silica layer 15, a LnPO₄ first transition layer, aAeAl₁₂O₁₉ second transition layer, and a AeAl₄O₇ outer layer; a siliconbond coat layer 14, an optional silica layer 15, a Ln₄Al₂O₉ firsttransition layer, a AeAl₁₂O₁₉ second transition layer, and a AeAl₄O₇outer layer; a silicon bond coat layer 14, an optional silica layer 15,a Lna₄Ga₂O₉ first transition layer 16, a AeAl₁₂O₁₉ second transitionlayer 16, and a AeAl₄O₇ outer layer 18; a silicon bond coat layer 14, anoptional silica layer 15, a HfO₂ transition layer 16, and a Ga₂O₃ outerlayer 18; a silicon bond coat layer 14, an optional silica layer 15, aLnPO₄ transition layer 16, and a Ga₂O₃ outer layer 18; a silicon bondcoat layer 14, an optional silica layer 15, a Ln₄Al₂O₉ transition layer16, and a Ga₂O₃ outer layer 18; a silicon bond coat layer 14, anoptional silica layer 15, a Lna₄Ga₂O₉ transition layer 16, and a Ga₂O₃outer layer 18; a silicon bond coat layer 14, an optional silica layer15, a Ln₄Al₂O₉ transition layer 16, and a BSAS outer layer 18; a siliconbond coat layer 14, an optional silica layer 15, a Ln₄Ga₂O₉ transitionlayer 16, and a BSAS outer layer 18; a silicon bond coat layer 14, anoptional silica layer 15, a Ln₄Al₂O₉ first transition layer 16, a BSASsecond transition layer 16, and a ZnAl₂O₄ outer layer 18; a silicon bondcoat layer 14, an optional silica layer 15, a Ln₄Ga₂O₉ first transitionlayer 16, a BSAS second transition layer 16, and a ZnAl₂O₄ outer layer18; a silicon bond coat layer 14, an optional silica layer 15, aLn₄Al₂O₉ first transition layer 16, a BSAS second transition layer 16,and a MgAl₂O₄ outer layer 18; a silicon bond coat layer 14, an optionalsilica layer 15, a Ln₄Ga₂O₉ first transition layer 16, a BSAS secondtransition layer 16, and a MgAl₂O₄ outer layer 18. As used herein, “Ae”represents the alkaline earth elements of magnesium (Mg), calcium (Ca),strontium (Sr), barium (Ba), and mixtures thereof As used herein,“mullite/BSAS mixture” refers to a mixture comprising from about 1% toabout 99% mullite and from about 1% to about 99% BSAS.

Similarly, in another embodiment, a silicon-containing component maycomprise a silicide bond coat layer 14. In this instance, the EBC maycomprise any of the previously listed architectures with the exceptionthat the silicon bond coat layer is replaced with a silicide bond coatlayer. In addition, when using a silicide bond coat layer 14, the EBCmay comprise on of the following architectures: a silicide bond coatlayer 14, an optional silica layer 15, a Ln₂Si₂O₇ first transition layer16, a BSAS second transition layer 16, and a ZnAl₂O₄ outer layer 18; asilicide bond coat layer 14, an optional silica layer 15, a Ln₂Si₂O₇transition layer 16, and a Ln₄Ga₂O₉ outer layer 18; a silicide bond coatlayer 14, an optional silica layer 15, a Ln₂Si₂O₇ transition layer 16,and a Ln₃Ga₅O₁₂ outer layer 18.

Alternately, in another embodiment, a silicon-containing component maycomprise an aluminide-alumina TGO bond coat layer 14. In thisembodiment, the EBC does not need a silica layer and may comprise one ofthe following architectures: an aluminide-alumina TGO bond coat layer 14and a AeAl₂O₁₉ outer layer 18; an aluminide-alumina TGO bond coat layer14 and an HfO₂ outer layer; an aluminide-alumina TGO bond coat layer 14and a LnPO₄ outer layer; an aluminide-alumina TGO bond coat layer 14,AeAl₂O₁₉ transition layer 16, and a AeAl₄O₇ outer layer 18; analuminide-alumina TGO bond coat layer 14 and a AeHfO₃ outer layer 18; analuminide-alumina TGO bond coat layer 14 and a AeZrO₃ outer layer 18; analuminide-alumina TGO bond coat layer 14 and a ZnAl₂O₄ outer layer 18;an aluminide-alumina TGO bond coat layer 14 and a MgAl₂O₄ outer layer18; an aluminide-alumina TGO bond coat layer 14 and a Ln₄Al₂O₉ outerlayer 18; an aluminide-alumina TGO bond coat layer 14, and a Lna₄Ga₂O₉outer layer 18; an aluminide-alumina TGO bond coat layer 14, and aLn₃Al₅O₁₂ outer layer 18; an aluminide-alumina TGO bond coat layer 14,and a Ln₃Ga₅O₁₂ outer layer 18; an aluminide-alumina TGO bond coat layer14, and a Ga₂O₃ outer layer 18; an aluminide-alumina TGO bond coat layer14, a BSAS transition layer 16, and a ZnAl₂O₄ outer layer 18; or analuminide-alumina TGO bond coat layer 14, a BSAS transition layer 16,and a MgAl₂O₄ outer layer 18; an aluminide-alumina TGO bond coat layer14, a BSAS transition layer 16, and a Ln₂Si₂O₇ outer layer 18; analuminide-alumina TGO bond coat layer 14, a BSAS transition layer 16,and a HfO₂ outer layer 18; an aluminide-alumina TGO bond coat layer 14,a BSAS transition layer 16, and a LnPO₄ outer layer 18; analuminide-alumina TGO bond coat layer 14, a BSAS transition layer 16,and a Ln₂SiO₅ outer layer 18; an aluminide-alumina TGO bond coat layer14, a HfO₂ transition layer 16, and a AeAl₂O₁₉ outer layer 18; analuminide-alumina TGO bond coat layer 14, a HfO₂ transition layer 16,and a AeHfO₃ outer layer 18; an aluminide-alumina TGO bond coat layer14, a HfO₂ transition layer 16, and a AeZrO₃ outer layer 18; analuminide-alumina TGO bond coat layer 14, a HfO₂ transition layer 16,and a ZnAl₂O₄ outer layer 18; an aluminide-alumina TGO bond coat layer14, a HfO₂ transition layer 16, and a MgAl₂O₄ outer layer 18; analuminide-alumina TGO bond coat layer 14, a HfO₂ transition layer 16,and a Ln₄Al₂O₉ outer layer 18; an aluminide-alumina TGO bond coat layer14, a HfO₂ transition layer 16, and a Lna₄Ga₂O₉ outer layer 19; analuminide-alumina TGO bond coat layer 14, a HfO₂ transition layer 16,and a Ln₃Al₅O₁₂ outer layer 18; an aluminide-alumina TGO bond coat layer14, a HfO₂ transition layer 16, and a Ln₃Ga₅O₁₂ outer layer 18; analuminide-alumina TGO bond coat layer 14, a HfO₂ transition layer 16,and a Ln₂Si₂O₇ outer layer 18; an aluminide-alumina TGO bond coat layer14, a HfO₂ transition layer 16, and a Ln₂SiO₅ outer layer 18; analuminide-alumina TGO bond coat layer 14, a HfO₂ transition layer 16,and a Ga₂O₃ outer layer 18; an aluminide-alumina TGO bond coat layer 14,a YPO₄ transition layer 16, and a AeAl₂O₁₉ outer layer 18; analuminide-alumina TGO bond coat layer 14, a YPO₄ transition layer 16,and a AeHfO₃ outer layer 18; an aluminide-alumina TGO bond coat layer14, a YPO₄ transition layer 16, and a AeZrO₃ outer layer 18; analuminide-alumina TGO bond coat layer 14, a YPO₄ transition layer 16,and a ZnAl₂O₄ outer layer 18; an aluminide-alumina TGO bond coat layer14, a YPO₄ transition layer 16, and a MgAl₂O₄ outer layer 18; analuminide-alumina TGO bond coat layer 14, a YPO₄ transition layer 16,and a Ln₄Al₂O₉ outer layer 18; an aluminide-alumina TGO bond coat layer14, a YPO₄ transition layer 16, and a Lna₄Ga₂O₉ outer layer 19; analuminide-alumina TGO bond coat layer 14, a YPO₄ transition layer 16,and a Ln₃Al₅O₁₂ outer layer 18; an aluminide-alumina TGO bond coat layer14, a YPO₄ transition layer 16, and a Ln₃Ga₅O₁₂ outer layer 18; analuminide-alumina TGO bond coat layer 14, a YPO₄ transition layer 16,and a Ln₂Si₂O₇ outer layer 18; an aluminide-alumina TGO bond coat layer14, a YPO₄ transition layer 16, and a Ln₂SiO₅ outer layer 18; analuminide-alumina TGO bond coat layer 14, a YPO₄ transition layer 16,and a Ga₂O₃ outer layer 18.

In embodiments utilizing an oxide component, neither a bond coat, nor asilica layer, is needed. As used herein throughout, “oxide component”includes oxide-oxide CMCs, monolithic alumina ceramics, and monolithicmullite ceramics. The following EBC architectures are thus possible foroxide components: a AeAl₂O₁₉ outer layer 18; an AeAl₂O₁₉ transitionlayer 16 and a AeAl₄O₇ outer layer 18; a AeHfO₃ outer layer 18; a AeZrO₃outer layer 18; a ZnAl₂O₄ outer layer 18; a MgAl₂O₄ outer layer 18; aLn₄Al₂O₉ outer layer 18; a Lna₄Ga₂O₉ outer layer 18; a Ln₃Al₅O₁₂ outerlayer 18; a Ln₃Ga₅O₁₂ outer layer 18; a Ga₂O₃ outer layer 18; a BSAStransition layer 16 and a ZnAl₂O₄ outer layer 18; a BSAS transitionlayer 16 and a MgAl₂O₄ outer layer 18; a BSAS transition layer 16, and aLn₂Si₂O₇ outer layer 18; a BSAS transition layer 16, and a LnPO₄ outerlayer 18; a BSAS transition layer 16, and a Ln₂SiO₅ outer layer 18; aHfO₂ transition layer 16, and a AeAl₂O₁₉ outer layer 18; a HfO₂transition layer 16, and a AeHfO₃ outer layer 18; a HfO₂ transitionlayer 16, and a AeZrO₃ outer layer 18; a HfO₂ transition layer 16, and aZnAl₂O₄ outer layer 18; a HfO₂ transition layer 16, and a MgAl₂O₄ outerlayer 18; a HfO₂ transition layer 16, and a Ln₄Al₂O₉ outer layer 18; aHfO₂ transition layer 16, and a Lna₄Ga₂O₉ outer layer 19; a HfO₂transition layer 16, and a Ln₃Al₅O₁₂ outer layer 18; a HfO₂ transitionlayer 16, and a Ln₃Ga₅O₁₂ outer layer 18; a HfO₂ transition layer 16,and a Ln₂Si₂O₇ outer layer 18; a HfO₂ transition layer 16, and a Ln₂SiO₅outer layer 18; a HfO₂ transition layer 16, and a Ga₂O₃ outer layer 18;a YPO₄ transition layer 16, and a AeAl₂O₁₉ outer layer 18; a YPO₄transition layer 16, and a AeHfO₃ outer layer 18; a YPO₄ transitionlayer 16, and a AeZrO₃ outer layer 18; a YPO₄ transition layer 16, and aZnAl₂O₄ outer layer 18; a YPO₄ transition layer 16, and a MgAl₂O₄ outerlayer 18; a YPO₄ transition layer 16, and a Ln₄Al₂O₉ outer layer 18; aYPO₄ transition layer 16, and a Lna₄Ga₂O₉ outer layer 19; a YPO₄transition layer 16, and a Ln₃Al₅O₁₂ outer layer 18; a YPO₄ transitionlayer 16, and a Ln₃Ga₅O₁₂ outer layer 18; a YPO₄ transition layer 16,and a Ln₂Si₂O₇ outer layer 18; a YPO₄ transition layer 16, and a Ln₂SiO₅outer layer 18; a YPO₄ transition layer 16, and a Ga₂O₃ outer layer 18.

Together, the previously described EBC layers can provide CMASmitigation capability to high temperature ceramic components such asthose present in gas turbine engines such as combustor components,turbine blades, shrouds, nozzles, heat shields, and vanes, which areexposed to temperatures of about 3000 F (1649° C.) during routine engineoperations.

Any bond coat layer 14, silica layer 15, transition layer 16, and outerlayer 18 present may be made using conventional methods known to thoseskilled in the art. More particularly, and regardless of the particulararchitecture of the EBC having CMAS mitigation capability, the substratecomponent can be coated using conventional methods known to thoseskilled in the art, including, but not limited to, plasma spraying, highvelocity plasma spraying, low pressure plasma spraying, solution plasmaspraying, suspension plasma spraying, chemical vapor deposition (CVD),electron beam physical vapor deposition (EBPVD), sol-gel, sputtering,slurry processes such as dipping, spraying, tape-casting, rolling, andpainting, and combinations of these methods. Once coated, the substratecomponent may be dried and sintered using either conventional methods,or unconventional methods such as microwave sintering, laser sinteringor infrared sintering.

Regardless of the architecture of the EBC having CMAS mitigationcapability, the benefits are the same. Namely, the inclusion of thepresent CMAS mitigation compositions can help prevent the EBC fromdegradation due to reaction with CMAS in high temperature engineenvironments. More particularly, these CMAS mitigation compositions canhelp prevent or slow the reaction of CMAS with the barrier coating thatcan form secondary phases that rapidly volatilize in steam.Additionally, the present CMAS mitigation compositions can help preventor slow the penetration of CMAS through the barrier coating along thegrain boundaries into a nonoxide, silicon-based substrate. Reaction ofCMAS with substrates such as silicon nitrate and silicon carbide evolvenitrogen-containing and carbonaceous gases, respectively. Pressure fromthis gas evolution can result in blister formation within the EBCcoating. These blisters can easily rupture and destroy the hermetic sealagainst water vapor provided by the EBC in the first instance.

The presence of the CMAS mitigation compositions described herein canhelp prevent or slow the attack of molten silicates on the EBC, therebyallowing the EBC to perform its function of sealing the ceramiccomponent from corrosive attack in high temperature steam. Moreover, theCMAS mitigation compositions can help prevent recession of the ceramiccomponent, and also any layers of the EBC that may be susceptible tosteam recession if CMAS reacts with it, to form steam-volatile secondaryphases. Dimensional changes of ceramic components due to steam recessioncan limit the life and/or functionality of the component in turbineengine applications. Thus, the CMAS mitigation compositions areimportant to allow the barrier coating to perform its functions; therebyallowing the ceramic component to function properly and for its intendedtime span. Additionally, any transition layers present can providemoderate to strong barriers to high temperature steam penetration. Thiscan help reduce the occurrence of a reaction between the layers of thebarrier coating. Multiple transition layers can be included to furtherhelp reduce the occurrence of interlayer reactions, which can ariseafter long-term thermal exposure of the barrier coating.

This written description uses examples to disclose the invention,including the best mode, and also to enable any person skilled in theart to make and use the invention. The patentable scope of the inventionis defined by the claims, and may include other examples that occur tothose skilled in the art. Such other examples are intended to be withinthe scope of the claims if they have structural elements that do notdiffer from the literal language of the claims, or if they includeequivalent structural elements with insubstantial differences from theliteral language of the claims.

1. An environmental barrier coating having CMAS mitigation capabilityfor silicon-containing components, the barrier coating comprising: abond coat layer comprising silicon or silicide; and an outer layerselected from the group consisting of Ln₄Al₂O₉, and Lna₄Ga₂O₉.
 2. Anenvironmental barrier coating having CMAS mitigation capability forsilicon-containing components, the barrier coating comprising: a bondcoat layer comprising silicon or silicide; a transition layer comprisingHfO2 or LnPO4; and an outer layer selected from the group consisting ofLn4Al2O9, Ln4Ga2O9, AeZrO3, AeHfO3, ZnAl2O4, MgAl2O4, Ln3Ga5O12,Ln2Al5O12, AeAl12O19, and Ga2O3.
 3. The barrier coating of claim 3wherein when the transition layer comprises LnPO4, the outer layerfurther comprises Ln2SiO5 or Ln2Si2O7.
 4. An environmental barriercoating having CMAS mitigation capability for silicon-containingcomponents, the barrier coating comprising: a bond coat layer comprisingsilicon or silicide; a transition layer comprising Ln4Al2O9 orLna4Ga2O9; and an outer layer selected from the group consisting ofLn2SiO5, AeZrO3, AeHfO3, ZnAl2O4, MgAl2O4, Ln3Ga5O12, Ln2Al5O12,AeAl12O19, Ga2O3, BSAS, HfO₂, and LnPO₄.
 5. An environmental barriercoating having CMAS mitigation capability for silicon-containingcomponents, the barrier coating comprising: a bond coat comprisingsilicon or silicide; a first transition layer selected from the groupconsisting of Ln4Al2O9, and Lna4Ga2O9; a second transition layerselected from the group consisting of AeAl12O19, and BSAS; and an outerlayer wherein when the second transition layer is AeAl12O19 the outerlayer is AeAl4O7 and wherein when the second transition layer is BSASthe outer layer is ZnAlO4, or MgAl2O4.
 6. An environmental barriercoating having CMAS mitigation capability for silicon-containingcomponents, the barrier coating comprising: a bond coat comprisingsilicon or silicide; a first transition layer selected from HfO2, orLnPO4; a second transition layer comprising AeAl12O19; and an outerlayer comprising AeAl4O7.
 7. An environmental barrier coating havingCMAS mitigation capability for silicon-containing components, thebarrier coating comprising: a bond coat layer comprising silicide; afirst transition layer comprising Ln2Si2O7; a second transition layercomprising BSAS; and an outer layer comprising ZnAl2O4.
 8. Anenvironmental barrier coating having CMAS mitigation capability forsilicon-containing components, the barrier coating comprising: a bondcoat layer comprising silicide; a transition layer comprising Ln₂Si₂O₇;and an outer layer selected from the group consisting of Ln₄Ga₂O₉, orLn₃Ga₅O₁₂.